Septic shock is a complex syndrome that results from serious infection often initiated by trauma and/or surgery and the body's response to microbiologic invation claims over 200,000 lives per year in the United States. While some patients with septic shock eventually succumb to multisystem organ failure, many die of refractory hypotension and cardiovascular collapse. A better understanding of the complex pathogenetic mechanisms leading to cardiovascular collapse is needed to further improve the care of patients with septic shock. The overall objective of the proposed research is to characterize the role of nitric oxide (NO) and NO synthase 3 (NOS3) in the myocardial dysfunction associated with sepsis. Studies supported by this grant will have four aims: (1) characterize the impact of NOS3 on myocardial dysfunction and survival in a murine sepsis model that closely mimics human peritonitis, (2) elucidate the mechanisms whereby cardiac NOS3 attenuates sepsis-induced myocardial oxidative stress, (3) examine the mechanisms responsible for the altered myofilament sensitivity to calcium during sepsis, and (4) assess the impact of NOS3 on sepsis- induced alteration of calcium handling protein and cardiomyocyte relaxation. Proposed studies will take advantage of genetically-modified mice and two complementary mouse models of sepsis, lipopolysaccharide-induced shock and surgically-induced diffuse peritonitis. Findings in genetically-modified mice will be confirmed using pharmacological agents including NO donor compound and xanthine oxidoreductase inhibitors. Myocardial function will be assessed at the levels of intact animal, isolated cardiomyocytes, and skinned-myofilaments. This proposal seeks to define largely unexplored impact of NOS3 on cardiac oxidative stress, myocardial dysfunction, and survival during sepsis. By understanding the role of cardiac NOS3 during sepsis, we anticipate that the proposed studies will provide important information leading to the development of new therapeutic strategies to improve the care of critically ill patients with myocardial dysfunction of sepsis.